1. Field of the Invention
The present invention concerns an x-ray examination method as well as an x-ray apparatus to implement the method.
2. Description of the Prior Art
Particularly in medical technology) imaging examination methods based on the acquisition of x-ray Images have increased for years. In general, the x-rays generated by an x-ray radiator are emitted in the direction of an x-ray exposure plane in which the x-ray radiation is detected. Classically, photographic x-ray films are used for detection of the x-ray radiation. More recently digital x-ray detectors also have been used as an alternative.
For the acquisition of the x-ray image, a subject to be examined, which for medical purposes normally is a body part of a patient, is positioned in the beam path of the x-ray radiation in front of the x-ray exposure plane. The image contrast results due to the spatially different strong attenuation of the x-rays penetrating the subject.
In order to reduce the radiation exposure of the patient during the x-ray acquisition a diaphragm is typically arranged in front of the x-ray radiator that gates an x-ray beam of a predetermined size from the total generated x-ray radiation. This ray beam is adjusted such that only the region of the subject to be examined, and a surface portion of the x-ray exposure plane behind this region is exposed with x-ray radiation. In contrast, the remaining spatial region is shadowed by the diaphragm from the x-ray radiation.
A conventional diaphragm has a number of diaphragm plates or lamellae that can be manually adjusted to set the size of the beam and thus the area to be exposed. In order to ease the adjustment of the diaphragm, the x-ray apparatus frequently is equipped with an optical adjustment aid, with a visible light source being operated in parallel with the x-ray radiator. The diaphragm is illuminated by this light source from behind (meaning in the propagation direction of the x-ray radiation) with visible light, so the light- and radiation-permeable diaphragm section of the diaphragm is projected in the x-ray exposure plane. The area to be exposed in the x-ray acquisition is thus visible as an illuminated area in the x-ray exposure plane. According to conventional technology, the plates of the diaphragm are now adjusted manually until the exposure area is congruent with the region of the subject to be examined, in particular with the body part of the patient to be examined.
The adjustment process, which is subsequently also designated as a “collimation”, is relatively time-consuming. This is disadvantageous insofar as the patient must remain substantially motionless during the gating and the subsequent exposure.
It is accordingly desirable to an x-ray examination method to enable a particularly rapid collimation, but the border of the area to be exposed should enclose the region to be examined as exactly as possible in order to reduce the radiation exposure to the largest possible extent. Using conventional technology, these requirements run counter to one another, particularly because manual adjustment of the collimator normally becomes increasingly more time-consuming the more precisely the area to be exposed is matched to the region to be examined.